The present invention relates to an optical amplifier; and, more particularly, to an optical amplifier incorporating therein an optical gain medium which is made of a low phonon energy glass doped with rare earth ions.
As is well known, in an optical transmission system using a wavelength division multiplexing method for enhancing an optical transmission capacity, a narrow gap between channels makes a transmission capacity deteriorated owing to an inherent nonlinear effect in an optical fiber. Therefore, it is preferable that a wavelength range of an optical signal spectrum should be broad in order to enlarge the transmission capacity. The wavelength range of a low optical loss is approximately 1,200xcx9c1,700 nm in a conventional transmission silica optical fiber, whereby the broad wavelength range, i.e., approximately 500 nm range, is capable of being used in an optical transmission. Thus, it is most important thing to make an optical amplifier operable in this broad wavelength range.
To make use of this broad range, i.e., 1,200xcx9c1,700 nm, a plurality of optical amplifiers has been researched and developed, of which ranges are 1,300 nm, 1,450 nm, 1,500xcx9c1,600 nm and 1,650xcx9c1,680 nm, respectively. However, there is no optical amplification system utilizing the wavelengths ranging from 1,600 nm to 1,650 nm.
Especially, an erbium (Er3+)-doped silicate fiber is used for the wavelength range less than approximately 1,600 nm. This is caused by a characteristic of an intra-4f-configurational energy level structure of erbium ions. Therefore, there has been no ion-doped optical amplifier system that can be used in a range of 1,600xcx9c1,650 nm so far.
In case of a thulium-doped fluoride fiber, the gain wavelength range of this fiber is over than approximately 1,650 nm so that it is also difficult to lower the range below 1,650 nm due to the characteristic of thulium ions.
Therefore, it is necessary to develop a new optical amplification system using the wavelength ranging from 1,600 nm to 1,650 nm.
It is, therefore, an object of the present invention to provide an optical gain medium for use in 1.6 xcexcm band by doping rare earth ions into a low phonon energy optical medium.
In accordance with one aspect of the present invention, there is provided an optical amplifier for amplifying an optical signal, comprising: a low phonon energy optical medium doped with praseodymium ions (Pr3+) for utilizing as a gain medium to the optical signal; and a pumping means for pumping the low phonon energy optical medium to thereby obtain an amplified optical signal in 1,600xcx9c1,700 nm range.
In accordance with another aspect of the present invention, there is provided an optical gain medium, comprising: a low phonon energy material; and praseodymium ions doped into the low phonon energy material.